Recently, RF ID tags and contactless IC cards or smartcards are spreading widely. RF ID tags are applicable to merchandise management systems, inventory management systems, physical distribution systems, and the like in compliance with the ISO 15693 standard. Contactless IC cards are applicable to resident registry cards in compliance with the ISO 14443 standard, electronic ticket cards in compliance with the FeliCa® system, employee ID cards, electronic money, and the like. Such RF ID tags and IC cards are read and written into by contactless reading and writing devices, i.e. reader/writer devices.
Passive information storage devices or media such as so-called passive RF ID tags and contactless IC cards include no battery, and hence are required to receive electric power which is electromagnetically induced by a carrier transmitted by a contactless reader/writer device. Thus, for example, when a contactless reader/writer device located at a gate transmits an RF command signal and receives an RF response signal, an RF ID tag or a contactless IC card at a distant position may not be able to receive the RF command signal. On the other hand, the contactless reader/writer device may not be able to detect an ID carried by the RF response signal due to the weakness of the transmission power of the RF response signal transmitted by the RF ID tag or the contactless IC card located at a distant position.
Japanese Patent Application Publication JP 2004-282522-A published on Oct. 7, 2004 by Kori describes an RF ID tag transmitting and receiving circuit. In the transmitting and receiving circuit, a decoding circuit of the RF ID tag transmitting and receiving circuit processes a plurality of pieces of encoded data which have been received via a plurality of receiving antennas and then demodulated, to decode the data transmitted as responses from an RF ID tag. Thus, the decoding circuit decodes the plurality of pieces of encoded data, so that high cannel quality is achieved.
Japanese Patent Application Publication JP 2005-197797-A published on Jul. 21, 2005 by Sato et al. describes an RF tag reader device and an antenna unit for the RF tag reader device. The RF tag reader device includes a control circuit for generating access information used for accessing RF tag information stored in an IC circuit of an RF tag circuit element attached to a target article; a transmission antenna for transmitting this access information to an antenna of the RF tag circuit element to thereby perform access; and an antenna unit having two receiving antennas for receiving a response signal transmitted in response to the transmitted access information. The two receiving antennas are connected in such a manner that their distances are adjustable.
Japanese Patent Application Publication JP 2002-100920-A published on Apr. 5, 2002 by Uchida describes an RF information processing apparatus. An RF tag reader/writer transmits and receives an RF signal to and from an RF tag. The RF tag reader/writer has a receiving antenna formed by a first divided antenna and a second divided antenna. In the first divided antenna, a plurality of small antenna coils are arranged in a plane in a checker board pattern, while these small antenna coils are connected in series in a drawn-with-one-stroke manner. The second divided antenna is arranged so as to face the first divided antenna. In this arrangement, a plurality of small antenna coils of the second divided antenna are arranged in a plane in a checker board pattern in such a manner that each small antenna coil does not face the small antenna coils of the first divided antenna. These small antenna coils are connected in series in a drawn-with-one-stroke manner. This reduces the number of possible collisions among RF communication media.
Japanese Patent Application Publication JP HEI 11-126240-A published on May 11, 1999 by Sasuga et al. discloses a reader/writer controller, in which in a state of receive ready, a power supply for a transmitter unit is intermittently turned ON for transmitting command data.